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Faculty Name : - Er. Neha Jain

Paper Name: - Fundamentals of Electronic devices

Paper Code:-EEC-301

Semester:-IInd

Lecture-1Objectives:-

1. To describe what a semiconductor is.2. Explain different types of semiconductor materials.3. Draw the atomic configuration of Si & Ge.

Semiconductor material:-

Semiconductors are a group of materials having electrical conductivities

intermediate between metals and insulators. It is significant that the conductivity of these

materials can be varied over orders of magnitude by changes in temperature, optical

excitation and impurity content.

Different type of semiconductor materials:-

Semiconductor materials are found in column IV and neighboring column of the

periodic table.

Semiconductor materials

Elemental material Compound material

eg. Column IV semiconductor

Si, Ge

Semiconductor material having wide verity optoelectronic propertiesBinary Compound compose of two element (GaAs)

Ternary Compound compose of three element (GaAsP)

Quaternary Compound compose of four element (I GaAsP)

III & V GaN, Gap, GaAs, InP

II & IV ZnS, InSb, CdS

IV Sic

SiGe

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Si Materials:-

Diamond lattice structure of Carbon

There is tetrahedral structure in diamond lattice. In this each atom is connected with 4

atoms.

Si Si Si Si

Si Si Si Si

Si Si Si Si

Si Si Si Si

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I

IIIII

IV

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Lecture-21.2: CRYSTAL LATTICES

Arrangements of atom in various solids

Types of solids:-

A Crystalline form of solid has periodically repeated arrangement of atoms.Amorphous solids have no periodic structure.Polycrystalline solids are composed of many small regions of single crystal

malarial.

Crystalline Amorphous Polycrystalline

Space lattice:-

A space lattice is defined as an infinite array of points in three dimensional spaces in

which each point is identically located with respect to the others.

Construction detail of polycrystalline solid:-

+ Nucleus

Electron

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Atom

Unit Cell

Unit Cell

Crystal

Polycrystalline solid

Two dimension space lattice-

Square array Rectangular array

b c

a

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Three dimensional space lattice :-

Unit cell

Or

Basis:-

The way of filling up of points in a space lattice by the atoms is known as Basis.

Space lattice +basis = unit cell

Unit cell:-

A unit cell is defined as the basic structural part in the composition of materials. It is

analogous to a brick used in the building construction.

Metallic Crystal Structure:-Cubic lattices :- Unit cell is a cubicvolume .

Cubic lattices:-

Simple cubic Body Centered Face Centered Cubic

Sc Bcc Fcc

a b c= = a b c

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Calculation of Radius :-

SC FCC

a

a a

2

a

R =

No. of atoms in a unit cell1

8 18

X= =

no. of atoms1 1

8 68 2

X X= + 1 3 4= + =

No. of atoms in a Unit cell1

8 1 28

X= + =

2a

3a

4 3R a=

3

4

aR =

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Atomic Packing fraction :- Volume of atoms in a Unit cell

Total Unit cell volume

Numerical:-For a bcc lattice of identical atom with a lattice constant of 5A

0, calculate the atomic

packing faction and radius of atom

Given 0a SA=

For bcc, 03 5 3

2.164 4

aR SA= = =

Volume of each atom3

3

0

4

3

42.5

R

A

=

=

Total no. of atom = 1at the center +1/8 at 8 corner in a unit cell1

1 8

82

X= +

=

Volume of atom in a unit cell 02 42.5X A=3

Atomic packing facture3

42.5 268%

5

X= =

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Lecture-3

Planes and directions

To describe the position of a plane or the direction of vector with in the lattice, we

first setup a coordinate system with the origin at the lattice point and axes are lined up with

the edges of the cubic unit cell. Miller evolved a method to designate a plane as Miller

Indices.

Miller IndicesThere are three integers describing a particular plane are found in the following ways

1. Find the intercepts of the place with the crystal axes.2. Take the reciprocals of the three integers and reduce these to the smallest set of

integers (h k l ).

3. Miller indices of the plane is (h k l ).Example- 1 Label the given plane

Soln:-

Given plane interception are2a, 4b & 1c

Intercepts with the crystal axes : 2 4 1

Reciprocal of these integers : 1

Reduce to the smallest integers

Multiplying by L.C.M : 2 1 4

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Example- 2

Directions:-A direction in a lattice is expressed as a set of three integers with the same

relationship as the component of vector in that direction and reduced to there smallest

value.

(100)(010)

(111) (001)

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()

(110)

Diamond lattice:-

The basic crystal structure for many important semiconductors is the FCC lattice

with a basis of two atoms, giving rise to the diamond structure.eg Si, Ge & C

In Diamond lattice

No. of atoms : 8 corner atoms, 6 face central atoms & 4 interpenetrated atoms

No. of atoms/unit cell=8*1/8+6*(1/2) +4=8 atoms.

(111)

P

(001) (011)

(010)

(110)

(100)

(010)

(101)

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In many compound semiconductors, atoms are arranged in a basic diamond structure. But

are different on alternating sites this is called a zinc blend structure.

The diamond structure can be thought of as an fcc lattice with an extra atom placed at

a/4+b/4+c/4 from each of the fcc atoms.

Eg

Calculate the volume density of Si atoms, given that the lattice constant of Si is5.43A

0, Calculate the aerial density of atoms on the 100 place.

Soln

for

8 corner lattice point, 6 face centered point & 4 interpenetrated atoms.

Number of atoms/calve = 8X1/8+6X1/2+4

= 1+3+4=8 atoms.

Volume density = 8

(5.43X10

-8

) =5X10

22

atoms/cm

3

Areal density of atoms on the (100) plane

Areal density = no. of atoms

Area of (100) plane

No. of atoms on (100) plane on one unit cell

= 1/4X4+1

Areal density = 1/4X4+1

(5.43X10-8

)2

= 6.8X1014cm-2